1. Field of the Invention
This invention relates to improved thermoplastic compositions. In another aspect, it relates to aromatic carbonate compositions having improved properties including low temperature impact strength and impact strength after heat aging, the improvements provided through the addition of functionalized elastomeric polymers.
2. Description of Art in the Field
Aromatic carbonate compositions are known to have excellent physical properties, particularly high impact resistance and heat resistance, and are known as "engineering plastics". However the performance of these compositions tend to suffer in the area of resistance to crack propagation. This deficiency is illustrated in notch sensitivity, brittle breaks and occasional catastrophic failure of molded or extruded parts. The tendency of some of these polycarbonate compositions to break in brittle fashion, particularly in low temperature usage or after continuous or intermittent exposure at high temperatures, is a significant limitation of utility. The tendency toward brittle break behavior can be characterized by the notched Izod test ASTM D-256-56. With a normal notch of 1/8 (3.2 mm) inch, unmodified polycarbonate compositions will show a decrease from notched Izod values at room temperature of about 80% when tested at temperatures of about -20.degree. C. Notched Izod values show a similar magnitude of decrease if the thickness of the sample is increased as little as 1/8 (3.2 mm) inch, to 1/4 (6.4 mm) inch, even at room temperature. Aging at temperatures of about 125.degree. C. for a period of about 4 hours shows similar results.
Consequently, there is much in the art concerned with improving the impact strength of aromatic carbonate and particularly polycarbonate compositions. A variety of additives have been added or suggested for addition to polycarbonates with some improvement in impact strength being obtained. U.S. Pat. No. 4,172,859 teaches toughened thermoplastic compositions of various materials including polycarbonate nresins admixed with about 1-40 wt. % of at least one random copolymer and sheared so as to disperse the random copolymers in the resin in a particle size of 0.01 to 3.0 microns. The random copolymer is said to be comprised of one or more monomers taken from eight classes of monomers, included within which are ethylene, propylene and non-conjugated dienes, specific examples being ethylene/propylene/1,4-hexadiene-g-maleic anhydride, ethylene/propylene/5-propenyl-2-norbornene-g-maleic anhydride, ethylene/propylene/1,4-hexadiene/norbornadiene-g-fumaric acid, ethylene/propylene/5-ethylidine-2-norbornene-g-fumaric acid (sic), and ethylene/propylene/1,4-hexadiene/5-ethylidiene-2-norbornene-g-fumaric acid (sic). Mixed polymers are said to include examples such as ethylene/propylene/1,4-hexadiene/norbornadiene with styrene/maleic anhydride and styrene/butadiene with ethylene/maleic anhydride. Improved notched Izod values as reportedly tested in accordance with ASTM-256-56 are taught and the improvement is said generally to be proportional to adherent sites in the polymeric component, the melt viscosity and molecular weight distribution.
U.S. Pat. No. 4,358,563 discloses a polycarbonate composition said to possess an improved thick section impact strength as measured by notched Izod. The improvement is said to arise from preparing an aromatic carbonate polymer endcapped with an XR moiety, where X is inclusive of derivatives of organic compounds such as phenol, carboxyl, carboxyl halides, R is an alkyl, alkenyl, aryl, etc., of about 5-20 carbons, and admixing with a polyolefin impact modifier. The polyolefins include, for example polyethylene, polypropylene, ethylene-propylene diene copolymers, etc.
U.S. Pat. No. 4,444,950 discloses the modification of polycarbonate compositions with excellent impact resistance and heat resistance to improve weld strength. The disclosed compositions are said to comprise (A) a polycarbonate resin and (B) a rubber modified copolymer with (C) an epoxy group containing olefin copolymer. (B) is said to comprise a graft copolymer of such as ethylene/propylene/non-conjugated diene copolymer, styrene/butadiene copolymer, etc., graft polymerized with monomers such as styrene, acrylonitrile, or an alkyl acrylate, and combined with a copolymer comprising these last-named monomers. (C) is said to be a copolymer of at least one unsaturated epoxy compound and at least one olefin with or without at least one ethylenically unsaturated compound, such as glycidyl methacrylate/ethylene/vinyl acetate copolymer or glycidyl methacrylate/ethylene copolymer.
European Patent Application No. 0 119 533 discloses polycarbonate resin compositions said to have improved impact strength, especially in thick sections, and resistance to environmental stress crazing and cracking. The improvements are attributed to the use of a modifier combination (b) comprising, e.g., (b) (i) a selectively hydrogenated linear copolymer of one or more blocks of a vinyl aromatic polymer segment, like polystyrene, and one or more blocks of an olefinic elastomer of butadiene, isoprene, etc., (b) (ii) an olefin-methacrylate copolymer like ethylene-methylmethacrylate or a methacrylate alone, and optionally (b) (iii) a polyolefin such as polyethylene, polypropylene, ethylene-propylene copolymers, polyisobutylene and EPDM copolymers.
European Patent Application No. 0 106 096 discloses polycarbonate resin compositions said to have improved resistance to environmental stress crazing and cracking. The improvements are attributed to the use of a modifier combination (b) comprising (i) a thermoplastic olefin polymer insoluble in the polycarbonate resin, such as polyethylene, polypropylene, polyisobutylene, copolymers of ethylene and propylene, and mixtures, and a linear low density polyolefin such as ethylene-butene-1.
European Patent Application No. 0 119 531 discloses polycarbonate resin compositions said to have improved impact strength, especially in thick sections, and weld line strength. The improvements are attributed to the use of certain acrylic-olefin co/terpolymers (c) prepared from olefins and acrylates or acrylics, e.g. ethylene-ethyl-acrylate, in a composition comprising a polycarbonate resin (a) and an olefin polymer or copolymer (b) such as polyethylene, polypropylene, ethylene-propylene copolymers, polyisobutylene, EPDM copolymers and linear low density polyolefins such as ethylene-butene-1.
In addition to the above it is known in the art that polymers containing alkenyloxazolines can be crosslinked to make novel polymers. U.S. Pat. No. 3,505,297 discloses the crosslinking and conversion of polymers containing alkenyloxazolines into infusible, water and solvent resistant polymers by reaction with a polycarboxylic acid, including polymers having plural carboxylic acid groups in the polymer molecule. The article "Coupling of reactive polystyrene and polyethylene in melts", by Baker and Saleem in Polymer, 1987, Vol. 28, No. 12, 2057-2062, discloses reacting polystyrene having oxazoline groups and polyethylene having carboxyl groups in a melt blend for the investigation of claims in the art of production of alloys having better impact strength and tensile properties than the ordinary polyethylene-polystyrene blends.
As indicated above there is a continuing need for novel means of improving various properties of polymer compositions including the impact strength of aromatic carbonate compositions. It is thus an object of the instant invention to provide novel functionalized elastomeric polymers that are useful as impact modifiers for polycarbonate compositions as well as to provide a means of improving the impact strength of these compositions. A further object thus, is achieving novel aromatic carbonate compositions having improved impact strength at low temperatures, in thicker sections and after continued exposure to high temperatures.